


An Exchange

by SnowCrisp



Category: Horus Heresy - Various Authors, Warhammer 40.000
Genre: Loss of Virginity, Other, Overstimulation, Porn Without Plot, Tentacle Sex, Tentacles, excessive cum, second chapter is artwork, tfw your eye isn’t actually the first thing you bartered away to the warp
Language: English
Status: Completed
Published: 2021-01-11
Updated: 2021-01-11
Packaged: 2021-03-10 19:14:45
Rating: Explicit
Warnings: No Archive Warnings Apply
Chapters: 2
Words: 2,598
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/28072293
Author URL: https://archiveofourown.org/users/SnowCrisp/pseuds/SnowCrisp
Summary: Magnus summons a demon for knowledge, but must exchange something in return.
Comments: 1
Kudos: 19





	1. Chapter 1

**Author's Note:**

> Completely shameless PWP because I really wanted Magnus to get stuffed with tentacles. Also because I thought it would be funny if he lost his virginity to a demon.

The creature, a being of constant-changing violets, magentas, and pinks, lifted its head. It was more correct to refer to it as a mass of tentacles, attached to a singular, beak-like mouth. The nameless creature opens its maw, baring rows of razor-sharp teeth in a mock smile. Its eyes shine a luminous gold, almost obscured by the coiling tendrils.

Magnus knelt outside his summoning circle, observing the creature. Others would call it a demon, but that was a word he prefers _not_ to use. Too many bad connotations. A product of a superstitious and ignorant age. While he was not afraid, this was the first being he summoned from the Great Ocean. He understood they could be dangerous, but if he kept himself calm and guarded, then the creature could not harm him.

“Your name,” Magnus demands.

“Mara...” It says, voice wet with saliva. “Sorcerers called me the demon of temptation. But do not my title fool you. I always make good on my offers. I have never left a Sorcerer unsatisfied. If you’d like, I can give you the finest riches and the most exquisite treasures.”

“Greed will not persuade me,” Magnus replies, rising to his full height. “I only wish for knowledge.”

“Summoning a creature like myself was a mistake then. I am no scholar. But I have some secrets that may interest you.” Mara’s eyes twitch, an expression of mocking glee.

“I make no mistakes. Tell me what you know.”

Mara clicks its tongue and brays a rumbling breath; its attempt at a laugh.

“My services are not _free_ , Sorcerer,” It leans closer, its long tongue darting out to lick its beak. “I will give you my knowledge, but you must give me something in return.”

“Tell me your conditions first.”

Magnus had studied records of men who summoned ‘demons’ and bartered away their souls. It always brought tragedy. But Magnus was different. He learned from those old stories. He would not sacrifice something so valuable for anything so simple. There was always something more valuable to discover, and he would not succumb to the same greed.

Mara grins, moving forward until it presses itself against the unseen barriers of his circle. Its tendrils press against it, trying to reach him.

“Your body.”

“I’m not sharing a body with you,” Magnus says, and Mara laughs.

“Dense! Like a mortal. No, I want _you._ ” The inflection on Mara’s words became slimy. Magnus steps back, struggling to mask his confusion.

“What do you mean?”

a“I sense you lack experience in carnal pleasures, despite your intelligence. So, I offer you a first experience. It will be mutually beneficial.” Mara’s tone was patronizing, as though it were explaining a complex theory to an insect. Despite the affront to his intellect, he was distracted by Mara’s offer. Magnus swallows, averting his gaze.

He turns elsewhere, idle hands plucking at the fibers of his robes. The carnal, curious part of him wanted to accept the offer. Yet, on one hand, the creature was likely deceiving him. Just as possible, the reward would not be worth it. Yet Magnus found himself intrigued. Excited, even. With so many limbs, Mara would make for an interesting experience. 

Magnus had always been curious about sexuality. But, absence free time, his easily distracted nature, and the size differences between himself and his peers left him with no personal experience. He had to settle for books, absorbing all the information he found. In fact, the original Prospero settlers had brought many books from ancient Terra. Some academic, and many… less so. The latter had its allure, feeding his ideas and fantasies.

“I will permit this,” Magnus says, turning and allowing his robes to slip to the floor. Mara lifts its head, making its grin seem wider.

“Yes, wonderful. Come closer, Sorcerer.”

“One condition,” Magnus thrust his spear forward, stopping shy of where Mara’s throat could be. “Try to kill me, and I will banish you before you can raise your first blow.”

“I had no intention of harming you,” One tendril wraps around his spear. “Now, set this down. No need for such things.”

Magnus does so. He kept the spear just outside, knowing he could snatch it in a hurry. Stepping inside the circle, Mara wastes no time seizing him with its tendrils. Two wrap around his wrists, raising his arms high. Magnus squirms in its grip, annoyed at the uncomfortable position. He tugs at one, causing Mara to growl.

“I will be gentle.” It insists. One tendril caresses his cheek, before moving down to his chest. It snakes past the crevice of his pectorals, down his abdomen, before tugging the hem of his loincloth. He felt another tendril slip down his back, snaking under his loincloth to tease his entrance. Magnus frowns, feeling Mara moving too soon. If he was going to do this, he wanted it to be _interesting_ , damn it. He knew from his reading that this was not the full extent of Mara’s capabilities.

Magnus yanks himself out of Mara’s grasp with a quick motion. He snatches one tendril in his fist, ripping away. Hissing, Mara encircles a tendril around Magnus’ neck, forcing him to look up.

“Do you want this or not? I will keep my promise not to harm you, but if you continue to be difficult, then I will throw you out unsatisfied.”

“Of course I do, but you have not attempted to stimulate me past the bare minimum.” He said. “If this is a mutually beneficial bargain, then I would like it to be pleasurable.”

Mara laughs. “What did you expect, Sorcerer? A kiss? I am not your lover. But, if you are so insistent on being pleasured, then _allow me_!”

More tendrils wrap around his arms and legs, binding his arms behind his back. It lifts off the ground, tendrils spreading his legs. Mara brings him closer, the other tendrils reaching for him.

While Magnus had attempted to remain stoic to show control, he could not stop himself from moaning when tendrils creep up his legs and press the insides of his thighs. Nor could he keep himself composed as the mass of tendrils gropes his entire form. Their teasing touch traces his muscles, from his pectorals to the skin above his groin. One tendril wraps around his nipple, circling his dark areola. Magnus groans, head rolling back in pleasure.

Already, his erection was growing, and Magnus began to buck his hips. Mara, sensing his desperation, curls a tendril around his loincloth and pulls it away, letting his aching cock free. It twitches in the cool air, trembling for attention. His face turns red hot when he sees another tendril come close, this time coiling around his cock.

It began to pump him at a slow, torturous pace. Magnus growls, dissatisfied, and bucks his hips for a quicker pace. Mara responds by stopping altogether. It rubs the tip around Magnus’ cockhead, teasing him further. Precum drips from his cock, allowing the tendril to lubricate him further. It resumes, but even slower.

“ _Damn you,_ ” Magnus breaths through gritted teeth, toes curling. “When I said I wanted you to stimulate me, that doesn’t mean you tease—”

A tendril shoves itself into his mouth, halting his speech. While annoyed by the rude gesture, he could not help but moan as Mara began to thrust while stroking his cock. The tendril in mouth tastes slick-no, what _could_ he describe it as? He had to record this later, _for research_. Magnus presses his tongue against its underside, trying to get a better taste. It tastes of seaweed, yet sweet enough to intoxicate his senses. The tendril pulls back out, then back in, creating a steady rhythm. Magnus, realizing what its doing, begins to bob his head with it, saliva dribbling down his chin. He hears a sound of approval from Mara, and Magnus feels a surge of pride at satisfying such a creature. He moves his head further until it hits the back of his throat, moaning. The tendril quivers and shudders, kneading against his tongue before pulling out.

Another tendril lifts his legs. The spit-slicked tendril moves behind him, pressing against his entrance. Magnus gulps once, taking a breath as the tendril teases his hole. It’s enough to send tingles throughout his body, tensing in preparation. 

He expects Mara to tease him further, but it slips inside. It was gentle, at least. His breath hitches, his body unsure of how to handle something so foreign. Yet despite that, his body quivers as Mara moves further. Magnus moans, sweat forming on his brow. When Mara hilts inside him, Magnus spends a few minutes catching his breath, cheeks warm with arousal.

Mara moves. It draws out and re-enters at a turtle’s pace, but increases until it was at a steady rhythm. The tendril at his cock still teases him, but its pace was increasing. Magnus moans, grateful that he was alone and no one around to hear his shame. 

Mara hits the deepest point of its thrust, squeezing his cock tight, and Magnus comes hard. He bucks his hips and thick strands of white cover his torso, limbs twitching in the aftermath. Mara continues, undeterred by Magnus’ orgasm until it comes itself. Magnus wasn’t even sure if Mara was capable of a climax until it trembles and pumps him with its thick seed.

Mara pulls out and relaxes Magnus’ legs, allowing seed to drip down his leg. Magnus pants, his body hot and blushing. He waits for Mara to place him on the ground, but a tendril lifts his head.

“That isn’t the end.” Mara laughs.

It shoves another tendril in his mouth, the sweet taste triggering his arousal. Magnus couldn’t resist the urge to suck it, sighing as it enters his throat. Mara turns him over, still fucking his mouth as tendrils rise to caress his body. Two rub his nipples, causing pinpricks of pleasure. More rise to wrap around his thighs and spread his legs, leaving him vulnerable. 

While Magnus focuses his attention on the tendril in his mouth, another teases his hole. He relaxes, waiting for Mara to ease itself in. Instead, it forces itself in with a single, strong thrust. He bites down. Mara growls, a tendril tangling in his hair and pulling.

“Don’t use your teeth.” Mara warns. It thrust harder, making his body shiver. The tendril at his cock adjusts its grip, squeezing him tight and brushing the underside of his balls. The mess of sensation makes it difficult for him to focus, his world becoming a haze.

The tendril in his mouth increases its pace, rubbing against his tongue in rapid movements. It twitches once, driving deep in his throat and exploding in his mouth. Magnus gags, struggling to pull his head back. Its seed tasted of stale saltwater, no sweetness to counter the bitter. It pulls out, its load landing on his face. The rest dribbles down his chin as Magnus coughs it up. He did not even get to catch his breath before another tendril shoves itself down his throat. Magnus groans, accepting the familiar taste of sweetness and seaweed on his tongue, as there was nothing else he could do. Then another hard thrust from behind, this time making his body jolt.

He shudders, eyes fluttering as pleasure overtook his senses. Magnus closes his eyes, trying to move his body as Mara’s pace increases. A quick, hard slam gives him equal parts pleasure and pain. He has to stop himself from biting down , relaxing his body and letting Mara pound into him. His cock twitches in its grasp, brushing against the tendrils with each forceful thrust. 

The tendril swells inside, somehow hitting pleasure spots he never knew he had. It trembles once more, bursting deep inside him. Excess seed drips out and down his legs. His head falls forward, moans muffled. Mara pulls his hair, bringing his head back. With little fanfare, his hips twitch and he spills himself, legs shaking. 

Another tendril replaces the old one, dislodging some excess seed. Some of it sloshes out, trickling down his leg as Mara continues its relentless pace. The tendril in his mouth grinds against his tongue and climaxes again, sticky and thick. This time, it refuses to withdraw, forcing Magnus to swallow. Mara finishes, pulls out, and lets the rest of its viscous seed paint his back. It replaces itself, repeating the process again. Magnus groans, now certain that Mara would not be satisfied until the rest of its tentacles had a turn with him. He closes his eyes, losing himself to pleasure.

How long had it gone on for? It was daylight when he summoned Mara, and well into night now. Mara had brought him close to its body. Magnus’ body was limp, exhausted after hours of repeated climaxes. Tendrils envelop him, groping his skin and rubbing against his skin. Some of them burst from grinding against him, fresh seed dripping down his reddened face and body. Mara licks his cheek, its tongue wet and slimy against his skin. Right as Mara comes inside him for the last time, it whispers in his ear, drops him to the ground, and disappears without a trace.

Magnus pants, his throat parched and muscles aching. Through his cloudy gaze, he sees his spear outside the circle, just as he left it. Though it looked miles away. Regardless, he pushes himself to his knees, body shaking. He takes his spear, his body pulsing with pain as he grips it in his hand. He stands, leaning against his spear-like an old man. Wincing, he steps forward, trying not to think about the seed dripping down his leg. 

‘ _I’ll write about this later._ ’ He tells himself, cringing as he takes another step. ‘ _After a drink and a long, hot bath_.’

* * *

Two hundred years later and Magnus hadn’t written it down. But not through a lack of trying. As soon as he pressed pen to paper, he realized how _foolish_ he looked. He sold his body for knowledge, which wasn’t even valuable, and all he had to show for it was a sore ass and a strange walk which persisted for a week afterward. So he opted to let it become an embarrassing memory. At least he could say his sexual encounters after were less embarrassing than that first venture.

In a brief time of levity between brothers, they share a drink together. They share their stories of their homeworlds, with Russ taking the lead. Somehow, it led to Russ bragging about his sexual conquests. Many of them were outlandish tales. _Then_ Russ felt it was a _great_ idea to ask how they all lost their virginities. That was when he remembers Mara. Magnus grips his cup, hard enough for cracks to form. His face burned hot, growing dark red. The memory tinged his tongue with the barest hint of saltwater. Russ, seeing his reaction, slaps his back, laughing all the while.

“Magnus, let’s start with you. How d’you lose your virginity on that dustbowl you call a homeworld? Or didja have to read about it?”

Russ laughs at his own joke, some of his brothers chuckling as well. Magnus did his best to mask his embarrassment. He swallows hard. 

“Of course I’ve read about it. Unlike you, I’d prefer to know what I’m getting into.”

Russ looks unconvinced, leaning closer. 

“Oh, _really_ now? Who was it with?”

“... A fellow scholar.” He lies, bringing the cup to his lips. “Very good with their hands.”

  
  



	2. The Art

Artwork drawn by Sxpaiscia, who you can find on [Twitter](https://twitter.com/Sxpaiscia1) and [Tumblr.](https://sxpaiscia.tumblr.com/) Full size [here](https://cdn.discordapp.com/attachments/775341898965188705/792788716921290772/magnus_tentacles_yay.jpg) ;)


End file.
